TypeScript 7 reference · Type Operators and Keywords

TypeScript unknown Keyword

The type-safe 'anything': a value of type unknown must be narrowed (checked) before you can use it, unlike any.

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Examples

Narrow before useTry it yourself

function parse(json: string): unknown {
  return JSON.parse(json);
}
const data = parse('{"name":"Ana"}');
// @ts-expect-error: unknown must be narrowed first
data.name;
if (typeof data === "object" && data !== null && "name" in data) {
  console.log(data.name);
}

Output

Ana

Errors in catch are unknownTry it yourself

try {
  throw new Error("boom");
} catch (err: unknown) {
  console.log(err instanceof Error ? err.message : String(err));
}

Output

boom

Version history

Version	Change
TypeScript 3.0	Added

never · The type with no values: for functions that never return, impossible branches, and exhaustiveness checks.
type predicates (x is T) · A function returning 'value is Type' tells TypeScript that the value has that type wherever the function returns true.
TypeScript keyof, typeof and Indexed Access · tutorial

Examples

Version history

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